Because of their excellent properties such as processability, chemical resistance, electrical properties and mechanical properties, crystalline thermoplastic resins such as polyolefins, polyesters, polyamides and polyacetals have been processed into, for example, injection molded articles, hollow molded articles, films, sheets and fibers for various uses. However, these products do not always have sufficient rigidity, thermal rigidity or transparency for some uses.
It is known that the rigidity, thermal rigidity and transparency of the molded articles formed from the crystalline thermoplastic resins may be improved by the rapid formation of fine crystals in the molding process. Therefore, crystal nucleating agents such as talc have been conventionally used to accelerate crystallization rates of crystalline thermoplastic resins.
However, not all the conventional crystal nucleating agents, provide the resins with sufficient crystallization rates, and thus the resulting molded articles do not have always satisfactory mechanical properties such as rigidity and thermal rigidity and/or optical properties such as transparency and glossiness.
For example, JP-A 58-160343 discloses polyester compositions which comprise polyethylene terephthalate or polyester containing a major amount of polyethylene terephthalate, and metallic salts of terpene carboxylic acids to increase crystallization rates of crystalline resins. This publication, however, does not teach or suggest which of the metallic acids of terpene carboxylic acids can provide the thermoplastic resins with the best effect in the increase of crystallization rates, and the molded articles with the best mechanical and/or optical properties.